Added in API level 21

ForkJoinPool

open class ForkJoinPool : AbstractExecutorService

kotlin.Any
↳	java.util.concurrent.AbstractExecutorService
	↳	java.util.concurrent.ForkJoinPool

An ExecutorService for running ForkJoinTasks. A ForkJoinPool provides the entry point for submissions from non-ForkJoinTask clients, as well as management and monitoring operations.

A ForkJoinPool differs from other kinds of ExecutorService mainly by virtue of employing work-stealing: all threads in the pool attempt to find and execute tasks submitted to the pool and/or created by other active tasks (eventually blocking waiting for work if none exist). This enables efficient processing when most tasks spawn other subtasks (as do most ForkJoinTasks), as well as when many small tasks are submitted to the pool from external clients. Especially when setting asyncMode to true in constructors, ForkJoinPools may also be appropriate for use with event-style tasks that are never joined.

A static commonPool() is available and appropriate for most applications. The common pool is used by any ForkJoinTask that is not explicitly submitted to a specified pool. Using the common pool normally reduces resource usage (its threads are slowly reclaimed during periods of non-use, and reinstated upon subsequent use).

For applications that require separate or custom pools, a ForkJoinPool may be constructed with a given target parallelism level; by default, equal to the number of available processors. The pool attempts to maintain enough active (or available) threads by dynamically adding, suspending, or resuming internal worker threads, even if some tasks are stalled waiting to join others. However, no such adjustments are guaranteed in the face of blocked I/O or other unmanaged synchronization. The nested ManagedBlocker interface enables extension of the kinds of synchronization accommodated.

In addition to execution and lifecycle control methods, this class provides status check methods (for example getStealCount) that are intended to aid in developing, tuning, and monitoring fork/join applications. Also, method toString returns indications of pool state in a convenient form for informal monitoring.

As is the case with other ExecutorServices, there are three main task execution methods summarized in the following table. These are designed to be used primarily by clients not already engaged in fork/join computations in the current pool. The main forms of these methods accept instances of ForkJoinTask, but overloaded forms also allow mixed execution of plain Runnable- or Callable- based activities as well. However, tasks that are already executing in a pool should normally instead use the within-computation forms listed in the table unless using async event-style tasks that are not usually joined, in which case there is little difference among choice of methods.

Summary of task execution methods

	Call from non-fork/join clients	Call from within fork/join computations
Arrange async execution	`execute(java.util.concurrent.ForkJoinTask)`	`ForkJoinTask#fork`
Await and obtain result	`invoke(java.util.concurrent.ForkJoinTask)`	`ForkJoinTask#invoke`
Arrange exec and obtain Future	`submit(java.util.concurrent.ForkJoinTask)`	`ForkJoinTask#fork` (ForkJoinTasks are Futures)

The common pool is by default constructed with default parameters, but these may be controlled by setting three System#getProperty:

java.util.concurrent.ForkJoinPool.common.parallelism - the parallelism level, a non-negative integer
java.util.concurrent.ForkJoinPool.common.threadFactory - the class name of a ForkJoinWorkerThreadFactory
java.util.concurrent.ForkJoinPool.common.exceptionHandler - the class name of a UncaughtExceptionHandler
java.util.concurrent.ForkJoinPool.common.maximumSpares - the maximum number of allowed extra threads to maintain target parallelism (default 256).

If a SecurityManager is present and no factory is specified, then the default pool uses a factory supplying threads that have no Permissions enabled. The system class loader is used to load these classes. Upon any error in establishing these settings, default parameters are used. It is possible to disable or limit the use of threads in the common pool by setting the parallelism property to zero, and/or using a factory that may return null. However doing so may cause unjoined tasks to never be executed.

Implementation notes: This implementation restricts the maximum number of running threads to 32767. Attempts to create pools with greater than the maximum number result in IllegalArgumentException.

This implementation rejects submitted tasks (that is, by throwing RejectedExecutionException) only when the pool is shut down or internal resources have been exhausted.

Summary

Nested classes
abstract	`ForkJoinWorkerThreadFactory` Factory for creating new `ForkJoinWorkerThread`s.
abstract	`ManagedBlocker` Interface for extending managed parallelism for tasks running in `ForkJoinPool`s.

Public constructors
`<init>()` Creates a `ForkJoinPool` with parallelism equal to , using the , no UncaughtExceptionHandler, and non-async LIFO processing mode.
`<init>(parallelism: Int)` Creates a `ForkJoinPool` with the indicated parallelism level, the , no UncaughtExceptionHandler, and non-async LIFO processing mode.
`<init>(parallelism: Int, factory: ForkJoinPool.ForkJoinWorkerThreadFactory!, handler: Thread.UncaughtExceptionHandler!, asyncMode: Boolean)` Creates a `ForkJoinPool` with the given parameters.

Public methods
open Boolean	`awaitQuiescence(timeout: Long, unit: TimeUnit!)` If called by a ForkJoinTask operating in this pool, equivalent in effect to `ForkJoinTask#helpQuiesce`.
open Boolean	`awaitTermination(timeout: Long, unit: TimeUnit!)` Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.
open static ForkJoinPool!	`commonPool()` Returns the common pool instance.
open Unit	`execute(task: ForkJoinTask<*>!)` Arranges for (asynchronous) execution of the given task.
open Unit	`execute(task: Runnable!)`
open Int	`getActiveThreadCount()` Returns an estimate of the number of threads that are currently stealing or executing tasks.
open Boolean	`getAsyncMode()` Returns `true` if this pool uses local first-in-first-out scheduling mode for forked tasks that are never joined.
open static Int	`getCommonPoolParallelism()` Returns the targeted parallelism level of the common pool.
open ForkJoinPool.ForkJoinWorkerThreadFactory!	`getFactory()` Returns the factory used for constructing new workers.
open Int	`getParallelism()` Returns the targeted parallelism level of this pool.
open Int	`getPoolSize()` Returns the number of worker threads that have started but not yet terminated.
open Int	`getQueuedSubmissionCount()` Returns an estimate of the number of tasks submitted to this pool that have not yet begun executing.
open Long	`getQueuedTaskCount()` Returns an estimate of the total number of tasks currently held in queues by worker threads (but not including tasks submitted to the pool that have not begun executing).
open Int	`getRunningThreadCount()` Returns an estimate of the number of worker threads that are not blocked waiting to join tasks or for other managed synchronization.
open Long	`getStealCount()` Returns an estimate of the total number of tasks stolen from one thread's work queue by another.
open Thread.UncaughtExceptionHandler!	`getUncaughtExceptionHandler()` Returns the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks.
open Boolean	`hasQueuedSubmissions()` Returns `true` if there are any tasks submitted to this pool that have not yet begun executing.
open T	`invoke(task: ForkJoinTask<T>!)` Performs the given task, returning its result upon completion.
open MutableList<Future<T>!>!	`invokeAll(tasks: MutableCollection<out Callable<T>!>!)`
open Boolean	`isQuiescent()` Returns `true` if all worker threads are currently idle.
open Boolean	`isShutdown()` Returns `true` if this pool has been shut down.
open Boolean	`isTerminated()` Returns `true` if all tasks have completed following shut down.
open Boolean	`isTerminating()` Returns `true` if the process of termination has commenced but not yet completed.
open static Unit	`managedBlock(blocker: ForkJoinPool.ManagedBlocker!)` Runs the given possibly blocking task.
open Unit	`shutdown()` Possibly initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.
open MutableList<Runnable!>!	`shutdownNow()` Possibly attempts to cancel and/or stop all tasks, and reject all subsequently submitted tasks.
open ForkJoinTask<T>!	`submit(task: ForkJoinTask<T>!)` Submits a ForkJoinTask for execution.
open ForkJoinTask<T>!	`submit(task: Callable<T>!)`
open ForkJoinTask<T>!	`submit(task: Runnable!, result: T)`
open ForkJoinTask<*>!	`submit(task: Runnable!)`
open String	`toString()` Returns a string identifying this pool, as well as its state, including indications of run state, parallelism level, and worker and task counts.

Protected methods
open Int	`drainTasksTo(c: MutableCollection<in ForkJoinTask<*>!>!)` Removes all available unexecuted submitted and forked tasks from scheduling queues and adds them to the given collection, without altering their execution status.
open RunnableFuture<T>!	`newTaskFor(runnable: Runnable!, value: T)`
open RunnableFuture<T>!	`newTaskFor(callable: Callable<T>!)`
open ForkJoinTask<*>!	`pollSubmission()` Removes and returns the next unexecuted submission if one is available.

Inherited functions

From class ExecutorService

`Boolean`	`awaitTermination(timeout: Long, unit: TimeUnit!)` Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.
`Boolean`	`isShutdown()` Returns `true` if this executor has been shut down.
`Boolean`	`isTerminated()` Returns `true` if all tasks have completed following shut down. Note that `isTerminated` is never `true` unless either `shutdown` or `shutdownNow` was called first.
`Unit`	`shutdown()` Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no additional effect if already shut down. This method does not wait for previously submitted tasks to complete execution. Use `awaitTermination` to do that.
`MutableList<Runnable!>!`	`shutdownNow()` Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution. This method does not wait for actively executing tasks to terminate. Use `awaitTermination` to do that. There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. For example, typical implementations will cancel via `Thread#interrupt`, so any task that fails to respond to interrupts may never terminate.

From class Executor

Unit

execute(command: Runnable!)

Executes the given command at some time in the future. The command may execute in a new thread, in a pooled thread, or in the calling thread, at the discretion of the Executor implementation.

From class AbstractExecutorService

`MutableList<Future<T>!>!`	`invokeAll(tasks: MutableCollection<out Callable<T>!>!, timeout: Long, unit: TimeUnit!)`
`T`	`invokeAny(tasks: MutableCollection<out Callable<T>!>!)`
`T`	`invokeAny(tasks: MutableCollection<out Callable<T>!>!, timeout: Long, unit: TimeUnit!)`

Properties
static ForkJoinPool.ForkJoinWorkerThreadFactory!	`defaultForkJoinWorkerThreadFactory` Creates a new ForkJoinWorkerThread.

Public constructors

<init>

Added in API level 21

ForkJoinPool()

Creates a ForkJoinPool with parallelism equal to , using the , no UncaughtExceptionHandler, and non-async LIFO processing mode.

Exceptions
`java.lang.SecurityException`	if a security manager exists and the caller is not permitted to modify threads because it does not hold `("modifyThread")`

<init>

Added in API level 21

ForkJoinPool(parallelism: Int)

Creates a ForkJoinPool with the indicated parallelism level, the , no UncaughtExceptionHandler, and non-async LIFO processing mode.

Parameters
`parallelism`	Int: the parallelism level

Exceptions
`java.lang.IllegalArgumentException`	if parallelism less than or equal to zero, or greater than implementation limit
`java.lang.SecurityException`	if a security manager exists and the caller is not permitted to modify threads because it does not hold `("modifyThread")`

<init>

Added in API level 21

ForkJoinPool(
    parallelism: Int, 
    factory: ForkJoinPool.ForkJoinWorkerThreadFactory!, 
    handler: Thread.UncaughtExceptionHandler!, 
    asyncMode: Boolean)

Creates a ForkJoinPool with the given parameters.

Parameters
`parallelism`	Int: the parallelism level. For default value, use `java.lang.Runtime#availableProcessors`.
`factory`	ForkJoinPool.ForkJoinWorkerThreadFactory!: the factory for creating new threads. For default value, use `defaultForkJoinWorkerThreadFactory`.
`handler`	Thread.UncaughtExceptionHandler!: the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks. For default value, use `null`.
`asyncMode`	Boolean: if true, establishes local first-in-first-out scheduling mode for forked tasks that are never joined. This mode may be more appropriate than default locally stack-based mode in applications in which worker threads only process event-style asynchronous tasks. For default value, use `false`.

Exceptions
`java.lang.IllegalArgumentException`	if parallelism less than or equal to zero, or greater than implementation limit
`java.lang.NullPointerException`	if the factory is null
`java.lang.SecurityException`	if a security manager exists and the caller is not permitted to modify threads because it does not hold `("modifyThread")`

Public methods

awaitQuiescence

Added in API level 21

open fun awaitQuiescence(
    timeout: Long, 
    unit: TimeUnit!
): Boolean

If called by a ForkJoinTask operating in this pool, equivalent in effect to ForkJoinTask#helpQuiesce. Otherwise, waits and/or attempts to assist performing tasks until this pool isQuiescent or the indicated timeout elapses.

Parameters
`timeout`	Long: the maximum time to wait
`unit`	TimeUnit!: the time unit of the timeout argument

Return
`Boolean`	`true` if quiescent; `false` if the timeout elapsed.

awaitTermination

Added in API level 21

open fun awaitTermination(
    timeout: Long, 
    unit: TimeUnit!
): Boolean

Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first. Because the never terminates until program shutdown, when applied to the common pool, this method is equivalent to but always returns false.

Parameters
`timeout`	Long: the maximum time to wait
`unit`	TimeUnit!: the time unit of the timeout argument

Return
`Boolean`	`true` if this executor terminated and `false` if the timeout elapsed before termination

Exceptions
`java.lang.InterruptedException`	if interrupted while waiting

commonPool

Added in API level 24

open static fun commonPool(): ForkJoinPool!

Returns the common pool instance. This pool is statically constructed; its run state is unaffected by attempts to or shutdownNow. However this pool and any ongoing processing are automatically terminated upon program System#exit. Any program that relies on asynchronous task processing to complete before program termination should invoke commonPool().awaitQuiescence, before exit.

Return
`ForkJoinPool!`	the common pool instance

execute

Added in API level 21

open fun execute(task: ForkJoinTask<*>!): Unit

Arranges for (asynchronous) execution of the given task.

Parameters
`task`	ForkJoinTask<*>!: the task

Exceptions
`java.lang.NullPointerException`	if the task is null
`java.util.concurrent.RejectedExecutionException`	if the task cannot be scheduled for execution

execute

Added in API level 21

open fun execute(task: Runnable!): Unit

Parameters
`command`	the runnable task

Exceptions
`java.util.concurrent.RejectedExecutionException`	if the task cannot be scheduled for execution
`java.lang.NullPointerException`	if the task is null

getActiveThreadCount

Added in API level 21

open fun getActiveThreadCount(): Int

Returns an estimate of the number of threads that are currently stealing or executing tasks. This method may overestimate the number of active threads.

Return
`Int`	the number of active threads

getAsyncMode

Added in API level 21

open fun getAsyncMode(): Boolean

Returns true if this pool uses local first-in-first-out scheduling mode for forked tasks that are never joined.

Return
`Boolean`	`true` if this pool uses async mode

getCommonPoolParallelism

Added in API level 24

open static fun getCommonPoolParallelism(): Int

Returns the targeted parallelism level of the common pool.

Return
`Int`	the targeted parallelism level of the common pool

getFactory

Added in API level 21

open fun getFactory(): ForkJoinPool.ForkJoinWorkerThreadFactory!

Returns the factory used for constructing new workers.

Return
`ForkJoinPool.ForkJoinWorkerThreadFactory!`	the factory used for constructing new workers

getParallelism

Added in API level 21

open fun getParallelism(): Int

Returns the targeted parallelism level of this pool.

Return
`Int`	the targeted parallelism level of this pool

getPoolSize

Added in API level 21

open fun getPoolSize(): Int

Returns the number of worker threads that have started but not yet terminated. The result returned by this method may differ from getParallelism when threads are created to maintain parallelism when others are cooperatively blocked.

Return
`Int`	the number of worker threads

getQueuedSubmissionCount

Added in API level 21

open fun getQueuedSubmissionCount(): Int

Returns an estimate of the number of tasks submitted to this pool that have not yet begun executing. This method may take time proportional to the number of submissions.

Return
`Int`	the number of queued submissions

getQueuedTaskCount

Added in API level 21

open fun getQueuedTaskCount(): Long

Returns an estimate of the total number of tasks currently held in queues by worker threads (but not including tasks submitted to the pool that have not begun executing). This value is only an approximation, obtained by iterating across all threads in the pool. This method may be useful for tuning task granularities.

Return
`Long`	the number of queued tasks

getRunningThreadCount

Added in API level 21

open fun getRunningThreadCount(): Int

Returns an estimate of the number of worker threads that are not blocked waiting to join tasks or for other managed synchronization. This method may overestimate the number of running threads.

Return
`Int`	the number of worker threads

getStealCount

Added in API level 21

open fun getStealCount(): Long

Returns an estimate of the total number of tasks stolen from one thread's work queue by another. The reported value underestimates the actual total number of steals when the pool is not quiescent. This value may be useful for monitoring and tuning fork/join programs: in general, steal counts should be high enough to keep threads busy, but low enough to avoid overhead and contention across threads.

Return
`Long`	the number of steals

getUncaughtExceptionHandler

Added in API level 21

open fun getUncaughtExceptionHandler(): Thread.UncaughtExceptionHandler!

Returns the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks.

Return
`Thread.UncaughtExceptionHandler!`	the handler, or `null` if none

hasQueuedSubmissions

Added in API level 21

open fun hasQueuedSubmissions(): Boolean

Returns true if there are any tasks submitted to this pool that have not yet begun executing.

Return
`Boolean`	`true` if there are any queued submissions

invoke

Added in API level 21

open fun <T : Any!> invoke(task: ForkJoinTask<T>!): T

Performs the given task, returning its result upon completion. If the computation encounters an unchecked Exception or Error, it is rethrown as the outcome of this invocation. Rethrown exceptions behave in the same way as regular exceptions, but, when possible, contain stack traces (as displayed for example using ex.printStackTrace()) of both the current thread as well as the thread actually encountering the exception; minimally only the latter.

Parameters
`task`	ForkJoinTask<T>!: the task
`<T>`	the type of the task's result

Return
`T`	the task's result

Exceptions
`java.lang.NullPointerException`	if the task is null
`java.util.concurrent.RejectedExecutionException`	if the task cannot be scheduled for execution

invokeAll

Added in API level 21

open fun <T : Any!> invokeAll(tasks: MutableCollection<out Callable<T>!>!): MutableList<Future<T>!>!

Parameters
`tasks`	MutableCollection<out Callable<T>!>!: the collection of tasks
`<T>`	the type of the values returned from the tasks

Return
`MutableList<Future<T>!>!`	a list of Futures representing the tasks, in the same sequential order as produced by the iterator for the given task list, each of which has completed

Exceptions
`java.lang.InterruptedException`	if interrupted while waiting, in which case unfinished tasks are cancelled
`java.lang.NullPointerException`	if tasks or any of its elements are `null`
`java.util.concurrent.RejectedExecutionException`	if any task cannot be scheduled for execution

isQuiescent

Added in API level 21

open fun isQuiescent(): Boolean

Returns true if all worker threads are currently idle. An idle worker is one that cannot obtain a task to execute because none are available to steal from other threads, and there are no pending submissions to the pool. This method is conservative; it might not return true immediately upon idleness of all threads, but will eventually become true if threads remain inactive.

Return
`Boolean`	`true` if all threads are currently idle

isShutdown

Added in API level 21

open fun isShutdown(): Boolean

Returns true if this pool has been shut down.

Return
`Boolean`	`true` if this pool has been shut down

isTerminated

Added in API level 21

open fun isTerminated(): Boolean

Returns true if all tasks have completed following shut down.

Return
`Boolean`	`true` if all tasks have completed following shut down

isTerminating

Added in API level 21

open fun isTerminating(): Boolean

Returns true if the process of termination has commenced but not yet completed. This method may be useful for debugging. A return of true reported a sufficient period after shutdown may indicate that submitted tasks have ignored or suppressed interruption, or are waiting for I/O, causing this executor not to properly terminate. (See the advisory notes for class ForkJoinTask stating that tasks should not normally entail blocking operations. But if they do, they must abort them on interrupt.)

Return
`Boolean`	`true` if terminating but not yet terminated

managedBlock

Added in API level 21

open static fun managedBlock(blocker: ForkJoinPool.ManagedBlocker!): Unit

Runs the given possibly blocking task. When ForkJoinTask#inForkJoinPool(), this method possibly arranges for a spare thread to be activated if necessary to ensure sufficient parallelism while the current thread is blocked in ManagedBlocker#block.

This method repeatedly calls blocker.isReleasable() and blocker.block() until either method returns true. Every call to blocker.block() is preceded by a call to blocker.isReleasable() that returned false.

If not running in a ForkJoinPool, this method is behaviorally equivalent to

<code>while (!blocker.isReleasable())
    if (blocker.block())
      break;</code>

If running in a ForkJoinPool, the pool may first be expanded to ensure sufficient parallelism available during the call to blocker.block().

Parameters
`blocker`	ForkJoinPool.ManagedBlocker!: the blocker task

Exceptions
`java.lang.InterruptedException`	if `blocker.block()` did so

shutdown

Added in API level 21

open fun shutdown(): Unit

Possibly initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no effect on execution state if this is the commonPool(), and no additional effect if already shut down. Tasks that are in the process of being submitted concurrently during the course of this method may or may not be rejected.

Exceptions
`java.lang.SecurityException`	if a security manager exists and the caller is not permitted to modify threads because it does not hold `("modifyThread")`

shutdownNow

Added in API level 21

open fun shutdownNow(): MutableList<Runnable!>!

Possibly attempts to cancel and/or stop all tasks, and reject all subsequently submitted tasks. Invocation has no effect on execution state if this is the commonPool(), and no additional effect if already shut down. Otherwise, tasks that are in the process of being submitted or executed concurrently during the course of this method may or may not be rejected. This method cancels both existing and unexecuted tasks, in order to permit termination in the presence of task dependencies. So the method always returns an empty list (unlike the case for some other Executors).

Return
`MutableList<Runnable!>!`	an empty list

Exceptions
`java.lang.SecurityException`	if a security manager exists and the caller is not permitted to modify threads because it does not hold `("modifyThread")`

submit

Added in API level 21

open fun <T : Any!> submit(task: ForkJoinTask<T>!): ForkJoinTask<T>!

Submits a ForkJoinTask for execution.

Parameters
`task`	ForkJoinTask<T>!: the task to submit
`<T>`	the type of the task's result

Return
`ForkJoinTask<T>!`	the task

Exceptions
`java.lang.NullPointerException`	if the task is null
`java.util.concurrent.RejectedExecutionException`	if the task cannot be scheduled for execution

submit

Added in API level 21

open fun <T : Any!> submit(task: Callable<T>!): ForkJoinTask<T>!

Parameters
`task`	Callable<T>!: the task to submit
`<T>`	the type of the task's result

Return
`ForkJoinTask<T>!`	a Future representing pending completion of the task

Exceptions
`java.util.concurrent.RejectedExecutionException`	if the task cannot be scheduled for execution
`java.lang.NullPointerException`	if the task is null

submit

Added in API level 21

open fun <T : Any!> submit(
    task: Runnable!, 
    result: T
): ForkJoinTask<T>!

Parameters
`task`	Runnable!: the task to submit
`result`	T: the result to return
`<T>`	the type of the result

Return
`ForkJoinTask<T>!`	a Future representing pending completion of the task

Exceptions
`java.util.concurrent.RejectedExecutionException`	if the task cannot be scheduled for execution
`java.lang.NullPointerException`	if the task is null

submit

Added in API level 21

open fun submit(task: Runnable!): ForkJoinTask<*>!

Parameters
`task`	Runnable!: the task to submit

Return
`ForkJoinTask<*>!`	a Future representing pending completion of the task

Exceptions
`java.util.concurrent.RejectedExecutionException`	if the task cannot be scheduled for execution
`java.lang.NullPointerException`	if the task is null

toString

Added in API level 21

open fun toString(): String

Returns a string identifying this pool, as well as its state, including indications of run state, parallelism level, and worker and task counts.

Return
`String`	a string identifying this pool, as well as its state

Protected methods

drainTasksTo

Added in API level 21

protected open fun drainTasksTo(c: MutableCollection<in ForkJoinTask<*>!>!): Int

Removes all available unexecuted submitted and forked tasks from scheduling queues and adds them to the given collection, without altering their execution status. These may include artificially generated or wrapped tasks. This method is designed to be invoked only when the pool is known to be quiescent. Invocations at other times may not remove all tasks. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Parameters
`c`	MutableCollection<in ForkJoinTask<*>!>!: the collection to transfer elements into

Return
`Int`	the number of elements transferred

newTaskFor

Added in API level 21

protected open fun <T : Any!> newTaskFor(
    runnable: Runnable!, 
    value: T
): RunnableFuture<T>!

Parameters
`runnable`	Runnable!: the runnable task being wrapped
`value`	T: the default value for the returned future
`<T>`	the type of the given value

Return
`RunnableFuture<T>!`	a `RunnableFuture` which, when run, will run the underlying runnable and which, as a `Future`, will yield the given value as its result and provide for cancellation of the underlying task

newTaskFor

Added in API level 21

protected open fun <T : Any!> newTaskFor(callable: Callable<T>!): RunnableFuture<T>!

Parameters
`callable`	Callable<T>!: the callable task being wrapped
`<T>`	the type of the callable's result

Return
`RunnableFuture<T>!`	a `RunnableFuture` which, when run, will call the underlying callable and which, as a `Future`, will yield the callable's result as its result and provide for cancellation of the underlying task

pollSubmission

Added in API level 21

protected open fun pollSubmission(): ForkJoinTask<*>!

Removes and returns the next unexecuted submission if one is available. This method may be useful in extensions to this class that re-assign work in systems with multiple pools.

Return
`ForkJoinTask<*>!`	the next submission, or `null` if none

Properties

defaultForkJoinWorkerThreadFactory

Added in API level 21

static val defaultForkJoinWorkerThreadFactory: ForkJoinPool.ForkJoinWorkerThreadFactory!

Creates a new ForkJoinWorkerThread. This factory is used unless overridden in ForkJoinPool constructors.

ForkJoinPool

Summary

Nested classes

Public constructors

Public methods

Protected methods

Inherited functions

Properties

Public constructors

<init>

<init>

<init>

Public methods

awaitQuiescence

awaitTermination

commonPool

execute

execute

getActiveThreadCount

getAsyncMode

getCommonPoolParallelism

getFactory

getParallelism

getPoolSize

getQueuedSubmissionCount

getQueuedTaskCount

getRunningThreadCount

getStealCount

getUncaughtExceptionHandler

hasQueuedSubmissions

invoke

invokeAll

isQuiescent

isShutdown

isTerminated

isTerminating

managedBlock

shutdown

shutdownNow

submit

submit

submit

submit

toString

Protected methods

drainTasksTo

newTaskFor

newTaskFor

pollSubmission

Properties

defaultForkJoinWorkerThreadFactory